System and method for detecting dialysis needle dislodgment

ABSTRACT

A system for detecting needle dislodgement includes a first sensor element, a second sensor element, and an alarm. The first sensor element attaches to an associated dialysis tubing having a needle connected at one end. The first sensor element also attaches to the associated dialysis tubing offset from the needle and a sterile field, which is an area on a leg or arm adjacent to where the needle is inserted, in a manner such that movement of the associated dialysis tubing results in movement of the first sensor element. The second sensor element secures to the arm or leg offset from the sterile field. The alarm is in communication with or includes at least one of the first sensor element and the second sensor element. The alarm generates a signal indicative of a position of the first sensor element with respect to the second sensor element.

BACKGROUND

Dialysis involves the removal of blood from a patient and the return ofthe blood after it has been cleaned by a dialysis machine. Typicaldialysis treatments require two needles: one needle for the withdrawalof blood and one needle for the return of blood to the patient. Thewithdrawal site is normally an artery. A needle connected with dialysistubing and pump are used to draw blood from the artery to the dialysismachine. It can be relatively simple to detect needle dislodgement fromthe artery using conventional air sensor technology. If air is beingdrawn through the pump, this can be detected and an alarm can be soundedto indicate needle dislodgement from the artery. The return lineincludes a needle with venous access connected with dialysis tubing. Ifthe venous needle becomes dislodged, the pump would typically not detectair and may continue to operate and continue to draw blood from thepatient.

A known device for detecting needle dislodgement, and especially venousneedle dislodgement, is described in US 2006/00130591. This known devicecan include a venous needle equipped with a photo sensor that is coveredwith an opaque patch. If the venous needle becomes dislodged, the photosensor is exposed to light, which can then result in a signal beingtransmitted to provide an alarm to the patient. Such a device is notparticularly suitable for patients who cover their arm with a blanket orwho perform nocturnal dialysis while sleeping in a dark bedroom.

Another known device described in US 2009/0082647 includes an accessneedle assembly including a butterfly mount, tubing, a venous accessneedle, a sleeve made from clear tubing, and an imbedded wire. Thebutterfly mount includes a detector circuit to detect the wire withinthe tubing. The sleeve is an electroactive sleeve that contains ametallic or magnetic component that is detectable by a proximity orHall-effect sensor. The butterfly mount and the detector circuit areprovided in the sterile field, which is near the venous needle entrypoint and thus requires sterilization prior to insertion of the venousaccess needle.

SUMMARY

In view of the foregoing, a system for detecting needle dislodgementincludes a first sensor element, a second sensor element, and an alarm.The first sensor element is configured to attach to an associateddialysis tubing having a needle connected at one end. The first sensorelement is also configured to attach to the associated dialysis tubingoffset from the needle and a sterile field, which is an area on a leg orarm adjacent to where the needle is inserted, in a manner such thatmovement of the associated dialysis tubing results in movement of thefirst sensor element. The second sensor element is configured to secureto the arm or leg offset from the sterile field. The alarm is incommunication with at least one of the first sensor element and thesecond sensor element. The alarm is configured to generate a signalindicative of a position of the first sensor element with respect to thesecond sensor element.

A method of detecting a needle dislodgement includes attaching a firstsensor element to a dialysis tubing having a needle at one end in amanner such that the first sensor element is offset from the needle. Themethod further includes positioning a second sensor element offset froma sterile field, which is an area on a leg or arm of the patientundergoing dialysis adjacent to where the needle is inserted. The methodfurther includes inserting the needle into the leg or arm at the sterilefield. The method further includes positioning the first sensor elementin proximity to the second sensor element, and monitoring a position ofthe first sensor element with respect to the second sensor element usinga controller or an alarm circuit. The method also includes generating analarm signal via the controller or the alarm circuit when the positionof the first sensor element with respect to the second sensor elementchanges indicating dislodgement of the needle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a system for detecting needledislodgement.

FIG. 2 is a side schematic view of a portion of the system for detectingneedle dislodgement depicted in FIG. 1.

FIG. 3 is a diagram of an alarm circuit for the system for detectingneedle dislodgement.

FIG. 4 is a perspective view of another system for detecting needledislodgement.

FIG. 5 is a side schematic view of a portion of the system for detectingneedle dislodgement depicted in FIG. 4.

FIG. 6 is a schematic depiction of a tether connector for the system fordetecting needle dislodgement depicted in FIG. 4 where a length of thetether is adjustable.

FIG. 7 is a schematic depiction of another tether connector for thesystem for detecting needle dislodgement depicted in FIG. 4 where thelength of the tether is adjustable.

FIG. 8 is a schematic view of another system for detecting needledislodgement.

FIG. 9 is a schematic view of another system for detecting needledislodgement.

FIG. 10 is a schematic view of another system for detecting needledislodgement.

DETAILED DESCRIPTION

FIG. 1 generally depicts a system 10 for detecting needle dislodgement.In FIG. 1, a needle (not visible) is inserted into a fistula in apatient's arm 12 on an arterial side of the fistula and is shown coveredby tape 14. The area of the arm 12 adjacent to where the needle isinserted is referred to as a sterile field 16, which needs to be cleanedand sterilized prior to insertion of the needle into the arm 12. Theneedle is attached at one end to a withdrawal line dialysis tubing 18which is attached to a dialysis machine (not shown). Blood is drawn fromthe needle connected with the withdrawal line dialysis tubing 18 andtransported through a pump (not shown) to a dialysis machine, and thenreturned to the patient through return line dialysis tubing 22 having aneedle (not visible) connected at one end, which is covered by tape 24.The needle connected with the return line dialysis tubing 22 enters thearm at a venous access sterile field 26 on a venous side of the fistula.

The portion of the system 10 to detect whether the venous needle, whichis covered by the tape 24, becomes dislodged will now be described. Afirst sensor element mount 40 attaches to the return line dialysistubing 22 offset from the needle, which is hidden under the tape 24,along the length of the return line dialysis tubing 22 in a manner suchthat movement of the return line dialysis tubing 22 results in movementof the first sensor element mount 40. When attached to the return linedialysis tubing 22, the first sensor element mount 40 is inhibited frommovement with respect to the return line dialysis tubing 22. In otherwords, if the return line dialysis tubing 22 moves, then the firstsensor element mount 40 moves with it. As one example, the first sensorelement mount 40 can be a U-shaped clip, or a similar clip or device,that can fasten onto the return line dialysis tubing 22 while notimpeding the flow of blood through the return line dialysis tubing 22.

A first sensor element 42 mounts to the first sensor element mount 40 ina manner such that movement of the first sensor element mount 40 resultsin movement of the first sensor element 42. The first sensor element 42can be a magnet or other component of a proximity sensor that cooperateswith a second sensor element 44 mounted to a non-sterile sensor mountingapparatus 46. The non-sterile sensor mounting apparatus 46 is configuredto secure to the arm 12, or even a leg, of the patient undergoingdialysis treatment. The non-sterile sensor mounting apparatus 46 isconfigured to secure to the arm 12 or leg offset from the venous accesssterile field 26. As such, the non-sterile sensor mounting apparatus 46and the components mounted thereto need not be sterilized whenperforming dialysis treatment. In the embodiment depicted in FIG. 1, thenon-sterile sensor mounting apparatus 46 is a cuff or band, which can besimilar to a blood pressure cuff without the inflatable bladder, havinghook and loop fasteners for securing to the arm 12 or leg of thepatient.

As mentioned above, the second sensor element 44 mounts to thenon-sterile sensor mounting apparatus 46. As such, the second sensorelement 44 is configured to secure to an arm or leg offset from thevenous access sterile field 26. The second sensor element 44 is attachedto the non-sterile sensor mounting apparatus 46 such that movement ofthe non-sterile sensor mounting apparatus 46 results in movement of thesecond sensor element 44. Where the first sensor element 42 is a magnet,the second sensor element 44 can be a Hall-effect sensor. In theembodiment illustrated in FIG. 1, the first sensor element 42 isconfigured to be positioned above the second sensor element 44 and thesecond sensor element 44 is configured to be positioned between thefirst sensor element 42 and the arm 12 (or leg) when the non-sterilesensor mounting apparatus 46, which can be a cuff, is secured to the arm12 (or leg) and the needle at the one end of the return line dialysistubing 22 is inserted into the venous access sterile field 26. The firstsensor element 42 need not necessarily cover the second sensor element44, but instead could be offset from but still above the second sensorelement 44 in relation to the arm 12 (or leg) to facilitate placement ofthe return line dialysis tubing 22.

With reference to FIG. 2, a third sensor element 60 can mount to thenon-sterile sensor mounting apparatus 46. In the illustrated embodiment,the third sensor element 60 is a contact switch 62, which is also shownin FIG. 3, which depicts an example of alarm circuit 64, which will bedescribed in more detail below. With reference back to FIG. 2, the thirdsensor element 60 can include a movable contact 66 positioned in acavity 68 of an actuator receptacle 72, which can be referred to as anon-sterile mounting apparatus and can be fixed to the non-sterilesensor mounting apparatus 46. With reference back to FIG. 1, a retainer74, which can be smaller than but similar in configuration to the firstsensor element mount 40, attaches to the return line dialysis tubing 22offset from the needle (disposed beneath the tape 24) and offset fromthe first sensor element mount 40. The retainer 74 can be a clip thataffixes to the return line dialysis tubing 22 in a manner such thatmovement of the return line dialysis tubing 22 results in movement ofthe retainer 74. With reference to FIG. 2, a fourth sensor element 76,which can be in the form of an actuator such as a snap-in button,connects with the retainer 74 for movement with the retainer 74. Thefourth sensor element 76 includes an extension 78 that is configured tobe received inside the cavity 68 provided in the actuator receptacle 72.When the extension 78 is received inside the cavity 68, the extension 78contacts the movable contact 66 so as to close the contact switch 62(FIG. 3).

With reference to FIG. 3, the alarm circuit 64 that is depicted isconfigured to generate a signal indicative of a position of the firstsensor element 42 with respect to the second sensor element 44. Thealarm circuit 64 is also configured to generate a signal indicative of aposition of the fourth sensor element 76 with respect to the thirdsensor element 60. A power source 82, such as a small voltage battery,can be provided on the non-sterile sensor mounting apparatus 46. Thepower source 82 connects with the second sensor element 44, which can bea Hall-effect sensor. When the second sensor element 44 detects thepresence of the first sensor element 42, which can be a magnet, thereturn line dialysis tubing 22 is in an appropriate position such thatno needle dislodgement is detected. If the needle connected with thereturn line dialysis tubing becomes dislodged, the first sensor element42 moves with respect to the second sensor element 44, such that thesecond sensor element 44 no longer detects the magnetic field of thefirst sensor element 42, which can result in power being delivered to aspeaker 84, which is part of the alarm circuit 64. An on/off switch 86,which can also be mounted to the non-sterile sensor mounting apparatus46 and is not depicted in the alarm circuit 64 diagram in FIG. 2, canalso be provided to turn the alarm circuit 64 on and off. The alarmcircuit 64 depicted in FIG. 3 also includes the contact switch 62 inelectrical communication with the speaker 84. The alarm circuit caninclude NOT gates 90, 92 and OR gates 94, 96 to allow either movement ofthe first sensor element 42 with respect to the second sensor element 44or movement of the fourth sensor element 76 with respect to the movablecontact 66, which is part of the third sensor element 60, to generate analarm signal, for example through the speaker 84.

Other indicators other than a speaker 84 can also be provided. Forexample, a light could be illuminated. Additionally, a wireless signalgenerator could be provided in addition to or in lieu of the speaker 84to wirelessly communicate with another device, such as a smart phone orthe dialysis machine, and the smart phone or dialysis machine canreceive the signal and generate an appropriate indicative signal for thepatient undergoing dialysis to indicate that the needle has dislodged.Additionally, the alarm circuit 64 could also provide a signal to thedialysis machine to turn off the pump when either movement of the firstsensor element 42 with respect to the second sensor element 44 ormovement of the fourth sensor element 76 with respect to the movablecontact 66 is detected.

With reference back to FIG. 1, the portion of the system 10 to detectwhether the arterial needle, which is covered by the tape 14, caninclude the same components as the portion of the system 10 to detectwhether the venous needle has dislodged. A first arterial sensor elementmount 140 can attach to the withdrawal line dialysis tubing 18 offsetfrom the arterial needle, which is not visible underneath the tape 14,in a manner such that movement of the withdrawal line dialysis tubing 18results in movement of the first arterial sensor element mount 140. Thefirst arterial sensor element mount 140 is also inhibited from movementwith respect to the withdrawal line dialysis tubing 18 when attached tothe withdrawal line dialysis tubing 18. The first arterial sensorelement mount 140 can be identical to the first sensor element mount 40described above.

A first arterial sensor element 142 mounts to the first arterial sensorelement mount 140 in a manner such that movement of the first arterialsensor element mount 140 results in movement of the first arterialsensor element 142. The first arterial sensor element 142 can beidentical to the first sensor element 42 and cooperate with a secondarterial sensor element 144 mounted to the non-sterile sensor mountingapparatus 46 in the same manner that the first sensor element 42cooperates with the second sensor element 44. The non-sterile sensormounting apparatus 46 is configured to secure to the arm 12 or leg alsooffset from the sterile field 16 for the arterial needle.

The second arterial sensor element 144 can be identical to the secondsensor element 44 and mounts to the non-sterile sensor mountingapparatus 46. The second arterial sensor element 144 is attached to thenon-sterile sensor mounting apparatus 46 such that movement of thenon-sterile sensor mounting apparatus 46 results in movement of thesecond arterial sensor element 144.

A third arterial sensor element (not visible but identical to the thirdsensor element 60) can mount to the non-sterile sensor mountingapparatus 46. The third arterial sensor element can be a contact switch162, which is also shown in FIG. 3. The third arterial sensor elementcan include a moveable contact (identical to the movable contact 66)positioned in a cavity of an actuator receptacle, which can be fixed tothe non-sterile sensor mounting apparatus 46. With reference back toFIG. 1, an arterial line retainer 174, which can be to the retainer 74,attaches to the withdrawal line dialysis tubing 18 offset from theneedle (disposed beneath the tape 14) and offset from the first arterialsensor element mount 140. The arterial line retainer 174 can be a clipthat affixes to the withdrawal line dialysis tubing 18 in a manner suchthat movement of the withdrawal line dialysis tubing 18 results inmovement of the arterial line retainer 174. A fourth arterial sensorelement 176, which can be in the form of a snap-in button, connects withthe arterial line retainer 174 for movement with the arterial lineretainer 174. The fourth arterial sensor element 176 includes anextension (not visible in FIG. 1, but identical to the extension 78 inFIG. 2) that is configured to be received inside the cavity provided inthe actuator receptacle. When the extension is received inside thecavity, the extension contacts the moveable contact so as to close thecontact switch 162 (FIG. 3).

With reference to FIG. 3, the alarm circuit 64 can include NOT gates190, 192 and OR gates 194, 96 to allow either movement of the firstarterial sensor element 142 with respect to the second arterial sensorelement 144 or movement of the fourth arterial sensor element 176 withrespect to the movable contact to generate an alarm signal, for examplethrough the speaker 84.

FIGS. 4 and 5 depict an alternative arrangement of a system 210 fordetecting needle dislodgement. The system 210 includes a first sensorelement 240 that attaches to the return line dialysis tubing 22 offsetfrom the needle, which is disposed beneath the tape 24, through a tether242, which connects with a tether connector 244. Movement of the returnline dialysis tubing 22 results in movement of the first sensor element240 due to the connection between the first sensor element 240 and thetether connector 244, which is fixed to the return line dialysis tubing22.

The first sensor element 240 attaches to a retainer 246 which can besimilar to the retainer 74 described above. The first sensor element 240can be an actuator in the form of a snap-in button having an extension256 similar to the extension 78 described above with reference to FIG.3.

A non-sterile sensor mounting apparatus 260, which can be similar to thenon-sterile sensor mounting apparatus 46 described above, is configuredto secure to the arm 12 or a leg of the patient undergoing dialysistreatment. The non-sterile sensor mounting apparatus is configured tosecure to the arm 12 or a leg of the patient offset from the sterilefields 16, 26. As illustrated, the non-sterile sensor mounting apparatus260 in FIG. 4 is a cuff, which has been described above in more detail.

A second sensor element 266 mounts to the non-sterile sensor mountingapparatus 260. The second sensor element 266 in the embodiment depictedin FIGS. 4 and 5 can be a contact switch similar to the third sensorelement 60 described above. The second sensor element 266 can include amoveable contact 268 similar to the movable contact 66 described above.The moveable contact 268 can be positioned within a cavity 272 providedin a button receptacle 274.

In addition to including components to detect dislodgement of the venousneedle, the system 210 can detect dislodgement of the arterial needle,if desired. The system can include a first arterial sensor element 280that attaches to the withdrawal line dialysis tubing 18 offset from thearterial needle, which is disposed beneath the tape 14, through a tether282, which connects with a tether connector 284. Movement of thewithdrawal line dialysis tubing 18 results in movement of the firstarterial sensor element 280 due to the connection between the firstarterial sensor element 280 and the tether connector 284, which is fixedto the withdrawal line dialysis tubing 18.

The first arterial sensor element 280 attaches to a retainer 286 whichcan be similar to the retainer 74 described above. The first arterialsensor element 280 is identical to first sensor element 240 in theillustrated embodiment. A second arterial sensor element (not visible),which is identical to the second sensor element 266 in the illustratedembodiment, mounts to the non-sterile sensor mounting apparatus 260.

In use, the patient inserts the arterial needle (not visible) at thesterile field 16 and covers the needle with tape 14. The patient theninserts the venous needle at the venous access sterile field 26 andcovers the venous needle with the tape 24. The non-sterile sensormounting apparatus 260 can then be secured to the arm 12 (or the leg) ofthe patient undergoing dialysis treatment outside of each sterile field16, 26. The tether connector 244 can then be connected to the returnline dialysis tubing 22 or can be already attached to the return linedialysis tubing 22 offset from the respective needle. The first sensorelement 240 can then be inserted into the button receptacle 274 suchthat the extension 256 is received within the cavity 272. The extension256 can then contact the moveable contact 268, thus closing an alarmcircuit, which is not shown but can take a similar configuration to thealarm circuit 64 shown in FIG. 3. The same procedure can be followedwith the first arterial sensor element 280. As such, if the first sensorelement 240 moves with respect to the second sensor element 266 (orfirst arterial sensor element 280 moves with respect to the secondarterial sensor element) a signal is generated and alarm can be providedto the patient.

The tethers 242, 282 can be adjustable in length. FIG. 6 is a schematicdepiction of the tether connector 244, and the tether connector 284 canhave a similar configuration. The tether 242 can wind around a wheel292, which is positioned in the tether connector 244 and can be biasedby a torsion spring (not shown) so as to retract the tether 242 withinthe tether connector 244 around the wheel 292. A button 294 or a similarmovable component that can be actuated by an operator is operativelyconnected to the wheel 292 to preclude rotation of the wheel 292 afterthe adjustment of the length of the tether 242 to a desired length.Alternatively and with reference to FIG. 7, the tether 242 could extendthrough the tether connector 244 and a clamping mechanism 298 could beprovided to adjust the length of the tether 242.

FIG. 8 depicts another embodiment of a system for detecting needledislodgement in which a first sensor element 340 attaches to the returnline dialysis tubing 22 offset from the needle (hidden by the tape 24)in a manner such that movement of the return line dialysis tubing 22results in movement of the first sensor element 340.

In this embodiment, an array board 342 is configured to support the arm12 (or leg) of a patient undergoing dialysis treatment. In thisembodiment, the array board 342 is also configured to support the arm 12(or leg) offset from the sterile fields 16, 26 in that the patient's arm12 or leg rests on the array board 342 with the sterile fields 16, 26spaced from an upper surface 344 of the array board 342. An array 346(schematically depicted as a grid on the upper surface 344) is providedon the array board 342.

A second sensor element 350 is affixed to the arm 12 (or leg) of apatient undergoing dialysis treatment offset from the venous accesssterile field 26. Adhesive or adhesive tape can be used to affix thesecond sensor element 350 to the arm 12 (or leg) of the patient and thuscan be considered a non-sterile mounting apparatus. The array 346 is inelectrical communication with the first sensor element 340 and thesecond sensor element 350 and is configured to communicate with acontroller 352 (schematically depicted) to determine a relative positionof the first sensor element 340 with respect to the second sensorelement 350. The controller 352 is in electrical communication with apower source (not shown). The array 346 can include a plurality ofsensors (for example at each intersection of the grid). The plurality ofsensors on the array 346 are configured to communicate with both thefirst sensor element 340 and the second sensor element 350 and toprovide a signal by way of the controller 352 to determine the locationof each sensor with respect to the grid. As such, the relative distancebetween the first sensor element 340 and the second sensor element 350can be determined. If the relative distance between the first sensorelement 340 and the second sensor element 350 changes above apredetermined threshold, this can be an indication that the needleattached to the return line dialysis tubing 22 has dislodged. Thecontroller 352 can then send a signal to an alarm circuit, which cangenerate an audible or visual indication perceptible by a human or anoff signal to the pump on the dialysis machine.

FIG. 9 depicts another embodiment of a system for detecting needledislodgement in which a first sensor element 440 attaches to the returnline dialysis tubing 22 offset from the needle (hidden by the tape 24)and the venous access sterile field 26 in a manner such that movement ofthe return line dialysis tubing 22 results in movement of the firstsensor element 440. A second sensor element 450 is affixed to the arm 12(or leg) of a patient undergoing dialysis treatment offset from thevenous access sterile field 26 using a cuff 452. Adhesive or adhesivetape can also be used to affix the second sensor element 450 to the arm12 (or leg) of the patient and thus each can be considered a non-sterilemounting apparatus. In the embodiment illustrated in FIG. 9, the firstsensor element 440 is configured to be positioned above the secondsensor element 450 and the second sensor element 450 is configured to bepositioned between the first sensor element 440 and the arm 12 (or leg)when the non-sterile sensor mounting apparatus 452, which can be a cuff,is secured to the arm 12 (or leg) and the needle at the one end of thereturn line dialysis tubing 22 is inserted into the venous accesssterile field 26. The first sensor element 440 need not necessarilycover the second sensor element 450, but instead could be offset frombut still above the second sensor element 450 in relation to the arm 12(or leg) to facilitate placement of the return line dialysis tubing 22.

In the embodiment depicted in FIG. 9, the first sensor element 440 canbe a magnet and the second sensor element 450 can be a magnetometer thatmeasures relative change of a magnetic field at a particular location.When the second sensor element 450 is a magnetometer, it can be inelectrical communication with a controller 454 (depicted schematicallyin FIG. 9), which is connected to a power source (not shown) such as abattery. The magnetometer can monitor the location of the first sensorelement 440. When the system is turned on the relative location of themagnet with respect to the magnetometer is determined. The controller454 can be configured, e.g., programmed, to detect a change in thelocation of the magnet with respect to the magnetometer that is greaterthan a predetermined threshold. When the controller 454 detects a changein the location of the magnet with respect to the magnetometer that isgreater than the predetermined threshold, the controller 454 cangenerate an alarm signal similar to the alarm signal described above.

FIG. 10 depicts another embodiment of a system for detecting needledislodgement in which a first sensor element 540 attaches to the returnline dialysis tubing 22 offset from the needle (hidden by the tape 24)and the venous access sterile field 26 in a manner such that movement ofthe return line dialysis tubing 22 results in movement of the firstsensor element 540. A second sensor element 550 is affixed to the arm 12(or leg) of a patient undergoing dialysis treatment offset from thevenous access sterile field 26. Adhesive or adhesive tape can be used toaffix the second sensor element 550 to the arm 12 (or leg) of thepatient and thus each can be considered a non-sterile mountingapparatus.

Similar to the embodiment depicted in FIG. 8, an array board 542 isconfigured to support the arm 12 (or leg) of a patient undergoingdialysis treatment. In this embodiment, the array board 542 is alsoconfigured to support the arm 12 (or leg) offset from the venous accesssterile field 26 in that the patient's arm 12 or leg rests on the arrayboard 542 with the venous access sterile field 26 spaced from an uppersurface 544 of the array board 542. At least two magnetometers 546 (fourmagnetometers are depicted in FIG. 10) are provided on the array board542. Each magnetometer 546 is in electrical communication with acontroller 552, which is connected to a power source (not shown) such asa battery.

In the embodiment depicted in FIG. 10, the first sensor element 540 andthe second sensor element 550 are each magnets. The magnetometers 546are each in electrical communication with the controller 554. Themagnetometers 546 monitor the location of the first sensor element 540with respect to the second sensor element 550. When the system is turnedon the relative location of the first sensor element 540 with respect tothe second sensor element 550 is determined. The controller 554 can beconfigured, e.g., programmed, to detect a change in the location of thefirst sensor element 540 with respect to the second sensor element 550that is greater than a predetermined threshold. When the controller 554detects a change in the location of the first sensor element 540 withrespect to the second sensor element 550 that is greater than thepredetermined threshold, the controller 554 can generate an alarm signalsimilar to the alarm signal described above.

It will be appreciated that various of the above-disclosed embodimentsand other features and functions, or alternatives or varieties thereof,may be desirably combined into many other different systems orapplications. Also that various presently unforeseen or unanticipatedalternatives, modifications, variations or improvements therein may besubsequently made by those skilled in the art which are also intended tobe encompassed by the following claims.

The invention claimed is:
 1. A system for detecting needle dislodgementcomprising: a first sensor element mount configured to attach to anassociated dialysis tubing having a needle connected at one end, thefirst sensor element mount being configured to attach to the associateddialysis tubing offset from the needle and a sterile field, which is anarea on a leg or arm adjacent to where the needle is inserted, in amanner such that movement of the associated dialysis tubing results inmovement of the first sensor element mount; a first sensor elementmounted to the first sensor element mount in a manner such that movementof the first sensor element mount results in movement of the firstsensor element; a second sensor element configured to secure to the armor leg offset from the sterile field; and an alarm in communication withat least one of the first sensor element and the second sensor element,the alarm being configured to generate a signal indicative of a positionof the first sensor element with respect to the second sensor element.2. The system of claim 1, wherein the first sensor element is a magnetand the second sensor element is at least one of a Hall-effect sensorand a magnetometer.
 3. The system of claim 2, further comprising anon-sterile mounting apparatus configured to secure to the arm or legoffset from the sterile field, wherein the second sensor element mountsto the non-sterile mounting apparatus.
 4. The system of claim 3, furthercomprising a dialysis tubing retainer configured to attach to theassociated dialysis tubing offset from the needle and the sterile fieldsuch that movement of the associated dialysis tubing results in movementof the dialysis tubing retainer and a non-sterile mounting apparatusretainer on the non-sterile mounting apparatus, wherein the dialysistubing retainer attaches to the non-sterile mounting apparatus retainer.5. The system of claim 3, further comprising a third sensor elementmounted to the non-sterile mounting apparatus, and a fourth sensorelement configured to attach to the associated dialysis tubing offsetfrom the needle in a manner such that movement of the associateddialysis tubing results in movement of the fourth sensor element.
 6. Thesystem of claim 5, wherein the alarm is configured to generate an alarmsignal when either the fourth sensor element is not in contact with thethird sensor element or when the second sensor element detects movementof the magnet with respect to the second sensor element above apredetermined threshold.
 7. The system of claim 1, further comprising anon-sterile mounting apparatus configured to secure to the arm or legoffset from the sterile field, wherein the second sensor element mountsto the non-sterile mounting apparatus, which is a cuff, adhesive oradhesive tape.
 8. The system of claim 7, wherein the first sensorelement is configured to be positioned above the second sensor elementand the second sensor element is configured to be positioned between thefirst sensor element and the arm or leg when the cuff is secured to thearm or leg and the needle at the one end of the associated dialysistubing is inserted into the sterile field.
 9. The system of claim 8,wherein the non-sterile sensor mounting apparatus is the cuff, furthercomprising a third sensor element mounted to the cuff and a fourthsensor element configured to attach to the associated dialysis tubingoffset from the needle in a manner such that movement of the associateddialysis tubing results in movement of the fourth sensor element,wherein the fourth sensor element is configured to contact the thirdsensor element when the cuff is secured to the arm or leg and the needleat the one end of the associated dialysis tubing is inserted into thesterile field.
 10. The system of claim 7, wherein the non-sterile sensormounting apparatus is the cuff, the first sensor element attaches to theassociated dialysis tubing offset from the needle through a tether. 11.The system of claim 10, wherein the tether connects with a tetherconnector that is configured to attach to the associated dialysis tubingoffset from the needle in a manner such that movement of the associateddialysis tubing results in movement of the tether connector.
 12. Thesystem of claim 11, wherein the tether is adjustable in length.
 13. Thesystem of claim 1, further comprising an array in electricalcommunication with the first sensor element and the second sensorelement and configured to communicate with a controller to determine arelative position of the first sensor element with respect to the secondsensor element.
 14. The system of claim 13, wherein the first sensorelement and the second sensor element are each magnets, and the arrayincludes at least two magnetometers.
 15. A method of detecting a needledislodgement, the method comprising: attaching a clip offset from asterile field, which is an area on a led or arm of a patient adjacent towhere a needle is to be inserted, the clip carrying a first sensorelement to a dialysis tubing having the needle at one end in a mannersuch that the first sensor element is offset from the needle;positioning a second sensor element offset from the sterile field;inserting the needle into the patient at the sterile field; positioningthe first sensor element in proximity to the second sensor element;monitoring a position of the first sensor element with respect to thesecond sensor element using a controller or an alarm circuit; andgenerating an alarm signal via the controller or the alarm circuit whenthe position of the first sensor element with respect to the secondsensor element changes indicating dislodgement of the needle.
 16. Themethod of claim 15, further comprising wrapping a cuff having the secondsensor element mounted thereto around the arm or leg offset from thesterile field.
 17. The method of claim 16, wherein a third sensorelement is mounted to the cuff, the method further comprising:positioning a fourth sensor element, which is connected with thedialysis tubing, in contact with the third sensor element.
 18. Themethod of claim 17, further comprising: monitoring whether the fourthsensor element is in contact with the third sensor element using thecontroller or the alarm circuit; and generating the alarm signal whenthe fourth sensor element is not in contact with the third sensorelement indicating dislodgement of the needle.
 19. The method of claim15, further comprising supporting the arm or leg on an array boardoffset from the sterile field, the array board including at least twomagnetometers or an array of sensors in electrical communication withthe first sensor element and the second sensor element and configured tocommunicate with the controller to determine a relative position of thefirst sensor element with respect to the second sensor element.